Testosterone (T) plays a role in the adult expression and maintenance of sexual dimorphisms across vertebrate taxa. Adult males and females do not always respond the same way to T manipulation, however. Sometimes these sexual dimorphisms are due to differences in T exposure during development, but the ubiquity of this developmental role for gonadal steroids is unclear. This study will test the hypothesis that sex differences in T exposure during development organize sex differences observed in adults in a lizard (Anolis carolinensis); the hormonal regulation of the development of brain and behavior in this species is completely unknown. First, because T exposure may result from maternal yolk T deposition, yolk T will be documented for male and female eggs. Second, to determine the source of T in the embryonic environment, both maternal plasma T across the ovulatory cycle (and whether it passes from mother to yolk) and embryonic T synthesis and metabolism will be documented. Third, the effects of T exposure on development will be assessed by treatment of eggs or juveniles with T, the antiandrogen flutamide, or appropriate controls. Then, behavioral interactions between consexual and heterosexual pairs will be documented to determine treatment effects on the development of male-typical behavior, and the brain and peripheral structures associated with male-typical behavior will be characterized.